Moisture-crosslinkable formulations are well known, particularly those, which are based on silyl-functionalized polymers. The silyl-functionalized polymers are prepared by conventional methods. One example is the reaction of polymers that have end groups having active hydrogen with isocyanates, particularly isocyanatoalkylalkoxysilanes. Another example is the reaction of isocyanate terminated polyurethane prepolymer with aminosilane. The reaction may be carried out with or without catalysts, which promote isocyanate reaction.
Silane condensation catalysts include numerous compounds, for example dialkyltin compounds such as dibutyltin dilaurate; various metal complexes (chelates and carboxylates), for example of titanium, bismuth, zirconium, amines and salts thereof; and other known acidic and basic catalysts as well. Known catalysts which promote the isocyanate reaction with hydroxyl groups are often those which also promote silane condensation, for example dialkyltin compounds and metal complexes (chelates and carboxylates) of bismuth and zinc, or tertiary amine compounds.
The disadvantage of all known processes for preparing silane-crosslinkable polymers is due to the fact that the polymers have to be handled under conditions including exclusion of moisture. In industrial practice this is associated with a high degree of complexity and is therefore expensive.
Accordingly, it is an object of the present invention to provide moisture curable silylated isocyanato-terminated polyurethane prepolymer compositions with out tin catalysts by using reduced toxicity alternatives in products that are suitable for use as sealants, adhesives and coatings.